Stabilizing a voltage?

[kirbyfanner]

Hi,

So after months of work my NES handheld is coming along but I'm down to the batteries. I'm using a retro entertainment system, a noac that normally runs at 6v. The screen I'm using from ads fruit also runs at 6v. I'd love to run the system off of four double a's but the res is replay finnicky and won't run off of 4 double a's alone. It runs fine off of a 9 volt with a 7806 but that's not really desirable. I want to stabilize the 6v from the batteries to prevent anymore than 6v but idk how. Most regulator designs seem to take a higher voltage and that'd require more than 4 double a's. I thnk I read something about Zener diodes but I'm unsure.

Anyways, thanks in advance guys, pics are coming soon.

 

[Hermaphroditus]

You could use a zener diode set for 6 volts and have it reverse biased. That said, if it runs on 6 volts and you plan on using 4 AA batteries you may run into problems. AA batteries have a nominal voltage of 1.5 V, but commonly operate lower. A zener diode keeps a higher voltage at around the zener breakdown voltage (so if you get a 6V zener and have a source that's varying from around 7V to 6V it'll keep it pretty constantly right around 6V, this isn't the most efficient thing in the world, but it works). Most regulators work by stepping down a voltage. You can find step up regulators, too, but they're usually not as efficient as switching step down regulators and will have a pretty strict limitation on current draw. That said, if you're planning on running it off of AA batteries you're not worried too much about the current draw.

I think your best bet here would be to just get some rechargable 3.7V AA size batteries and have 2 in series parallel with another 2 in series. You'd then have a 7.4V source with a ~1600 mah rating. Not the best, but it's around what you were looking at for the AA batteries. And this would be cheaper in the long run, even with having a protection circuit and smart charger thrown in. And what's more, you can use standard AA size battery holders for it, too. This is an example, but there are more than just these floating about.

Edit: Oh yeah, if you decide to go with the 3.7V batteries, then you can either use a zener with a breakdown voltage of around 6V, a 7806, or (preferably) a switching regulator set to 6V output. That said, if it says it can run on 6V I'd give it a try to see if it can run on 7.4. Because if it can run on 7.4 you just need to have filtration circuitry and can neglect a regulator. If you decide to test this, I would get a fuse rated for around the maximum current draw your device is rated for, put it in series with the batteries, and then run the system. If it blows the fuse then I'd wager to say that it can't handle 7.4V.

Actually...3.7V batteries charge up to around 4.1V when fully charged, so I'd try it with around 8.2V to be completely safe. It's only like 2V over so it may not hurt it, but it's best to test before you just do. If you find it doesn't work then I'd say try to find a switching regulator. If you can't find a good switching regulator or don't want to get one, then you can either use a zener or 7806, but both of those are significantly less efficient.

 

[kirbyfanner]

That's so helpful, thanks so much! Yeah I'm gonna shoot for recharge bales I don't really know how to work with them though but I'm sure it won't be that hard

 

[Hermaphroditus]

No problem. Working with rechargable batteries isn't much different than working with nonrechargable. If you go for the AA sized ones you could actually get away with using a AA holder and just have them in there when they're good to go, and take them out to a separate charging station when you want to charge them. If you did this you could also buy 8 batteries instead of 4 and have one set charged at all times. Keep in mind, even when doing this you need some overdischarge protection circuit to keep the batteries from being too far drained. If you'd prefer to have them internal then you will need to wire up a general protection circuit in the device and have a charging port and a switch to have it charging or playing. There're plenty of diagrams throughout the site on how to do this.

 

[superben51]

Or, you could use a step-up regulator to increase the voltage and use a step-down reg to drop it down again. It's not the best but it works.

 

[Hermaphroditus]

Well it may work. Step up regulators cut the overall maximum draw pretty hard, then the step down regulator does it again. If you were to use AA's you would get pretty crappy battery life more than likely. It'd be cheaper in the long run to just spring for some rechargable lithium based cells at 3.7V each.

With using a step up and a step down you also run into the space problem even more. Granted, with rechargable lithium batteries you run into some spacing issues with protection circuits plus a regulator, but protection circuits are pretty darn small, and you can get away with really small step down regulators. But step up regulators are usually a bit larger and take a bit bigger of an inductor, so you'd be saving a bit of room and money in the long run springing for rechargable.

 

[andrew82]

Search in Google, there are many step-up and step-down dc to dc convertor are available as per your requirement. Texas instrument s has many dc to dc convertors. One is mentioned below for your reference - http://www.ti.com/lit/ds/symlink/lm2577.pdf

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